An ab initio study of the interaction of SCN- with a silver electrode:: The prediction of vibrational frequencies

Experimental results for the adsorption frequencies of SCN- on a silver electrode obtained with the surface-enhanced Raman spectrometry (SERS) method are presented and discussed. These results were confronted with a quantum chemical DFT-based study. Different clusters were used from the simple monoatomic case to a much more realistic representation of the silver electrode by means of a Ag-23 cluster simulating the (100) surface. The calculations were performed at the B3PW91/LanL2DZ and the BP86/TZP level. The interaction energies indicate the importance of the cluster size and calculation level. The cluster size was increased until the results were converged. Calculated vibrational frequencies for the different possible adsorption geometries on a (100) surface are compared with experiment. Together with the interaction energy results, they indicate that the preferred interaction via the sulfur atom on a hollow site of the silver electrode is in agreement with the hard and soft acids and bases principle.